LNG has recently gained significant attention as an alternative clean energy source as the cost of crude oil has reached historic highs. Thus, it is not surprising that global consumption of natural gas is projected to increase substantially in the coming years, and that the anticipated demand may not be met by domestic production. Natural gas shortage is further compounded by the retirement of older power plants and replacement with more efficient combined cycle power plants. To satisfy at least part of the increasing LNG demand, various LNG import terminals are being developed in North America, and existing facilities are expanded to accommodate a higher LNG throughput.
Use of LNG in a power plant as a fuel typically requires that the LNG is vaporized before combustion. Unfortunately, vaporization is an energy intensive process and typically requires a heat duty representing about 2 to 3% of the energy content in the LNG. While conventional LNG regasification facilities typically require an external heat source (e.g., seawater heater), the heat for vaporization may also be provided by a combustion process in a synergistic manner. For example, the vaporized LNG in an LNG regasification facility can be used to fuel a power plant, eliminating gas pipeline transmission costs, while the waste heat from the power plant can supply the heating duty of LNG. Thus, there are economic incentives to locate a power plant close to an LNG regasification terminal.
For example, U.S. Pat. Nos. 4,036,028 and 4,231,226 to Mandrin and Griepentrog, respectively, describe integration of a power plant with LNG regasification. Similar plants are reported in published U.S. Pat. App. No. 2003/0005698 and WO 02/097252 to Keller, U.S. Pat. No. 6,374,591, WO 96/38656, WO 95/16105, EP 0828925, and EP 0683847 to Johnson et al., and U.S. Pat. No. 6,367,258 and WO 01/07765 to Wen et al. Further substantially similar configurations are described in EP 0009387 to Mak or EP 0605159 to Tomlinson et al. In such known configurations, heat for regasification of LNG is provided by a heat exchange fluid, which is in thermal exchange with gas turbine intake, flue gas exhaust, and/or a working fluid of a power cycle. Such configurations are thought to improve the efficiency of the gas turbine cycle (Brayton cycle) by densifying the inlet air, thereby increasing its power output and efficiency. However, these processes are typically limited to cool the intake air to 40° F. (or higher) to avoid water freezing of the intake air.
Recently, various new configurations have been proposed that recover power at the LNG receiving terminal in which LNG is used as a heat sink for power generation, and/or as fuel to a power plant as described in our copending International patent applications with the serial numbers PCT/US03/25372 (published as WO 2004/109206) and PCT/US03/26805 (published as WO 2004/109180), and U.S. provisional patent application having Ser. No. 60/588,275, all of which are incorporated by reference herein.
It should be noted that while some of the above configurations provide benefits of reducing fuel consumption in LNG regasification using heat derived from gas turbine exhaust, the gain in power generation efficiencies is often not significant. Still further, and among yet other difficulties, heat transfer in some of these configurations is often limited by the freezing of water. Moreover, dislodging of ice particles from the turbine inlet tends to damage the gas turbine and disrupts power generation. Moreover, while the currently known gas turbine air pre-cool methods improve power generation efficiencies in hot climate regions (e.g., in the tropics or sub-tropics), they are often not suitable to colder climate regions (e.g., northeastern parts of North America). Even in relatively hot climate, such configurations provide efficiency benefits only in the summer months, with decreasing benefits in the winter seasons. Worse yet, in some cases operation of these units must be discontinued when the ambient temperatures drop below 40° F. to avoid water freezing at the air intake.
Therefore, while numerous processes and configurations for power plants with LNG utilization and/or regasification are known in the art, all of almost all of them suffer from one or more disadvantages. Thus, there is still a need to provide improved configurations and methods for power plants with LNG utilization and regasification.